Research in this grant is designed to apply behavioral techniques to the study of polydrug abuse. Reinforcement and discriminative-stimulus control functions will be used to evaluate the abuse potential of drugs in an attempt to understand the behavioral basis for polydrug abuse. The primary research aims are to advance the behavioral methodology for studying drug seeking behavior; to investigate the reinforcement and discriminative-stimulus control functions of drugs taken alone or in combination; and to follow-up research participants to determine whether or not response patterns exhibited in the laboratory relate to drug seeking behaviour outside the laboratory.